Underground Parking with Steel Sheet Piles – Comparative Study

Efficient and cost-effective solutions for urban Underground Parking Construction

Urban development faces numerous challenges, as city populations grow faster than the available housing. Major cities struggle to strike a balance between expansion and the well-being of their residents. 

Noise and traffic congestion near construction sites are also negative aspects of building activity, making the duration of construction projects a critical factor to be considered from the planning stage. 

Steel components offer the advantage of being prefabricated offsite, delivered ready for installation, and immediately subjected to loads. Experience shows that the construction speed of steel-based solutions, such as sheet piles, can be twice as fast as with other materials.

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In 2022, ArcelorMittal commissioned the German engineering firm GRBV Ingenieure im Bauwesen to delve into this topic and conduct a detailed comparison of various alternatives for constructing the outer wall of a two-level underground car park under typical northern German soil conditions. An inner-city location with adjacent buildings was selected as the context for the study.

When selecting a structural solution, several key indicators must be considered, with construction costs being the most critical. The cost estimates are based on preliminary structural designs where parameters such as geometry, soil characteristics, groundwater levels, and excavation base levels are standardised for all wall systems. The study analysed the following construction variants:

  • V1: Permanent sheet pile wall (SPW)
  • V2: Temporary sheet pile wall (SPW t.)
  • V3: Secant pile wall (BPW)
  • V4: Diaphragm wall (SLW)

The sheet pile wall, costing €1.15 million, emerged as the most cost-effective solution. The cost difference is approximately 25% compared to the secant pile wall and about 39% compared to the diaphragm wall. When considering the complete construction of the underground car park, total costs range between €3.1 million for the sheet pile wall solution and €3.6 million for the diaphragm wall solution.

The total cost calculation does not account for potential revenue losses due to reduced usable floor area. However, this factor is significant and should be considered when choosing a construction method. The evaluation of the variants includes a comparison of the usable floor area provided.

Furthermore, the final assessment incorporates additional criteria such as maintenance costs, construction time, logistics, execution risks, and sustainability. These criteria are weighted differently to reflect their relative importance.